Add tls_client example (#305)

* Add tls_client example

This requires pico_mbedtls in the pico-sdk
Connects to worldtimeapi.org and retrieves a web page
Originally written by Floris Bos @maxnet

pico_w/CMakeLists.txt

@@ -33,6 +33,12 @@ if (PICO_CYW43_SUPPORTED) # set by PICO_BOARD=pico_w
             add_subdirectory(tcp_server)
             add_subdirectory(freertos)
             add_subdirectory(udp_beacon)
+
+            if (NOT PICO_MBEDTLS_PATH)
+                message("Skipping tls examples as PICO_MBEDTLS_PATH is not defined")
+            else()
+                add_subdirectory(tls_client)
+            endif()
         endif()
     endif()
 endif()